Volumetric effects in the degradation of dimethacrylate-based polymer/filler nanocomposites: A positron annihilation study

• Published in: Polymer degradation and stability Vol. 176; p. 109150
• Main Authors: Shpotyuk, Oleh, Ingram, Adam, Shpotyuk, Yaroslav, Filipecki, Jacek, Shpotyuk, Olha
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01-06-2020; Elsevier BV
• Subjects: Algorithms; Atomic structure; Composite materials; Degradation; Dental materials; Direct conversion; Electron states; Light curing; Nanocomposites; Parameterization; Photopolymerization; Physical ageing; Polymer/filler nanocomposites; Polymers; Positron annihilation; Positron annihilation lifetime spectroscopy; Positronium; Spectra; Spectrum analysis; Trapping; Volumetric effects; Degradation; Physical ageing; Polymer/filler nanocomposites; Positron annihilation lifetime spectroscopy; Photopolymerization; Light curing; Volumetric effects
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2020.109150

The applicability of positron annihilation lifetime (PAL) spectroscopy to identify volumetric changes in nanostructured polymer/filler substances is first verified at the example of commercially available dimethacrylate-based dental restorative composites Charisma® (Heraeus Kulzer GmbH, Germany) affected to light-curing photopolymerization and one-year dry physical ageing. Principal channel governing PAL spectra in these nanocomposites is recognized as mixed positron-Ps trapping, where positronium Ps (i.e. bound positron-electron state) decay occurs in free-volume holes localized preferentially in polymer matrix, while free positron self-annihilation is character for interfacial voids at the surface of filler-particles assemblies in the filler and/or mixed filler-polymer environment. Methodological algorithm for experimental PAL spectra refinement referred to as the x3-x2-CDA (coupling decomposition algorithm) is validated for these nanocomposites, obeying changes in atomic-deficient structure due to direct conversion between positron-trapping and Ps-decaying sites. Straightforward parameterization of the reconstructed PAL spectra allows meaningful identification of free-volume entities responsible for nanostructurization-driven transformations.
•Degradation in polymer/filler systems by positron annihilation lifetime (PAL) spectra.•PAL spectroscopy of volumetric effects in dimethacrylate-based dental nanocomposites.•Inverse positron-to-Ps trapping conversion under light-curing photopolymerization.•Direct Ps-to-positron trapping conversion under dry physical ageing in nanocomposites.